MOTION OF THE HEART AND BLOOD 



as arteries. The arteries receive blood from the 

 veins in no other way than by transmission through 

 the heart, as previously said. So by ligating the 

 aorta close to the heart, there need be no uncer- 

 tainty about finding the arteries empty if they be 

 opened in the neck or elsewhere, and the veins 

 filled. 



The reason is now apparent why so much blood is 

 found in the veins in anatomical dissection, and 

 so little in the arteries, so much in the right side 

 of the heart, so little in the left. This fact prob- 

 ably led the ancients to believe that arteries con- 

 tained only spirits during an animal's life. The 

 reason for the difference is probably as follows.* 

 There is no other passage from the veins to the 

 arteries except through the heart and lungs, so 

 when an animal expires and the lungs stop moving, 

 the blood is prevented from passing from the pul- 

 monary artery to the pulmonary vein and then 

 into the left ventricle of the heart. This is like 

 what was noted previously in the embryo, where 

 the transit is prevented by the lack of motion in the 

 lungs and the opening and closing of its tiny pores. 

 The heart, however, does not stop at the same time 



* One reason has already been given. Is this an interpolation, 

 or addition to the original draft? There is much evidence that the 

 book was not composed as a whole, but that it is a combination of 

 many scattered notes written at different times. Respiration is 

 quite a factor in maintaining circulation. Dr. R. M. Waters, well- 

 known anesthetist, has told me of several instances where artificial 

 respiration has maintained a circulation when the heart has failed. 



[79I 



